Sing a song of slime mold

Originally published 15 November 1993

I sing of slime electric.

The armies of those I love engirth me and I engirth them, they will not let me off till I respond to them, and dis­cor­rupt them, and charge them full with the charge of the soul.

OK, I’m bor­row­ing from Walt Whit­man. These slight­ly mod­i­fied lines of his famous poem “I Sing the Body Elec­tric” are per­fect for intro­duc­ing my paean to slime molds.

A paean? A song of praise? You bet. Slime molds are unde­served­ly cor­rupt­ed by their name. Dou­bly corrupted.

But wait. Watch. Observe their stream­ings and slith­er­ings and tow­er­ings. They are a mass of indi­vid­u­als. They are a soci­ety. They blos­som like flo­ra. They creep about like fau­na. They are plant and ani­mal. And nei­ther. They embody in their life cycle the his­to­ry of life, and the his­to­ry of our race. They are charged full with animation.

For years, I have been fas­ci­nat­ed by micropho­tographs of slime molds in sci­en­tif­ic books and arti­cles. Recent­ly, I acquired my own colony of Dic­tyostelium dis­coideum, the researcher’s favorite slime mold. I observed their life cycle with a microscope.

With Whit­manesque gush, I sing their praises.

At first they are invis­i­ble, an uncount­able army of free-roam­ing amoe­bas, sin­gle-celled organ­isms, graz­ing on bacteria.

They mul­ti­ply by fis­sion­ing, split­ting down the mid­dle, two from one. Again. And again. Their pop­u­la­tion soars. Their food becomes scarce.

Trig­gered by hunger, some among them secrete a chem­i­cal called acrasin, after Acra­sia, the cru­el witch in Spenser’s The Faerie Queene who attract­ed men and turned them into beasts. It is a call. A sig­nal. The amoe­bas gath­er in the tens of thou­sands, stream­ing in gleam­ing rivers to the assem­bly point, becom­ing vis­i­ble in their slimy congregations.

Sur­ren­der­ing their indi­vid­u­al­i­ty, they heap them­selves into a gooey blob half-a-mil­lime­ter high. The blob falls onto its side, becom­ing a slug-like crea­ture. Some amoe­bas know they are ante­ri­or; oth­ers resigns them­selves to bring up the rear. The front end of the slug lifts as if to sniff the wind. The crea­ture slith­ers on a film of slime toward light and warmth.

As it slith­ers, the cells begin to change. The ante­ri­or cells are des­tined to become a stalk; the pos­te­ri­or cells will become spores.

A bright, warm place is found. The slith­er­ing ceas­es. Ante­ri­or cells push down through the spore mass, becom­ing a slen­der pil­lar anchored at the base, lift­ing a per­fect sphere of spores into the air. Some­times sev­er­al spheres are strung along a sin­gle stalk, like tiny rain­drops on a spi­der’s thread. The spores are dor­mant amoe­bas that will trav­el on the air when the sphere bursts asun­der to form new colonies. The stalk amoe­bas will die; they have sac­ri­ficed them­selves that oth­ers might live.

The fruit­ing tow­er is beau­ti­ful. Glit­ter­ing. Translu­cent. An Ozmi­an minaret, some­times as tall as this let­ter i. Fifty thou­sand amoe­bas pool their indi­vid­ual resources to build a repro­duc­tive spire.

What is this thing? Is it a plant? An ani­mal? A fun­gus? Are the slug and the tow­er con­gre­ga­tions of one-celled organ­isms that have tem­porar­i­ly sur­ren­dered their inde­pen­dence, or are they a mul­ti­celled organ­ism whose repro­duc­tive spores only tem­porar­i­ly live on their own?

These ques­tions have long exer­cised biol­o­gists. It is now wide­ly agreed that slime molds are nei­ther plant nor ani­mal nor fun­gus but mem­bers of the king­dom Pro­toc­tista, which encom­pass­es some of the most ancient sin­gle-celled organ­isms. Yet slime molds have char­ac­ter­is­tics of plants, ani­mals, and fun­gi. In their delight­ful inclu­sive­ness, they are a pre­cis of all life on Earth.

They even repro­duce on a micro-scale the social his­to­ry of humankind: nomad hunters and gath­er­ers band­ing togeth­er to build cities and raise tow­ers, spe­cial­iz­ing for dif­fer­ent occupations.

More fun­da­men­tal­ly, in their curi­ous life cycle slime molds reca­pit­u­late that episode in the his­to­ry of life, which occurred about 700 mil­lion years ago, when sin­gle-celled microor­gan­isms, hav­ing lived on their own for 3 bil­lion years, came togeth­er to form mul­ti­cel­lu­lar organ­isms. Invis­i­ble life became glo­ri­ous­ly vis­i­ble, and won­der­ful­ly diverse. Crea­tures indi­vid­u­al­ly small­er than the point of a pin piled them­selves togeth­er to become, in the full­ness of time, bron­tosaurus­es and blue whales.

There is a sense, I sup­pose, in which you and I are slime molds of a sort, accre­tions of bil­lions of cells that have band­ed togeth­er and spe­cial­ized for the pur­pose of pro­duc­ing sperms and ova. The essence of life is to make more life. Over an over again in the his­to­ry of life the effi­cien­cy of repro­duc­tion has been aid­ed by col­lab­o­ra­tion, sym­bio­sis, even altruism.

The stalk cells of a slime mold do not know that they are sac­ri­fic­ing their own lives to lift their spore cousins so that they might be more effi­cient­ly dis­persed, no more than the hun­dreds of types of spe­cial­ized cells in our own bod­ies know that their col­lec­tive evo­lu­tion­ary pur­pose is to pro­duce a few suc­cess­ful sperms or ova. But they do it. Is it altru­ism? Call it life. A great dri­ving ener­gy implic­it in mat­ter itself, the green fuse, the com­pul­sive inevitabil­i­ty of animation.

A gooey colony of Dic­tyostelium dis­coideum has per­formed its mar­velous trans­for­ma­tion on the stage of my micro­scope. I admire them, engirth them, and dis­cor­rupt them. Whit­man-like, I sing their prais­es. They are charged full with the charge of the soul.